Method of producing foundry moulds and cores

ABSTRACT

A method of producing foundry moulds and cores comprising the steps of preparing a mixture containing a moulding sand, an ingredient chosen from the group which consists of ligno sulphonate of an alkali, alkali-earth metal, ammonium and their mixture as a binder, a material containing aluminate of an alkali metal as a hardener and water, making moulds and cores from said mixture and weathering to harden. The material containing aluminate of an alkali metal is an intermediate product obtainable in the production of aluminum oxide from bauxite or nepheline ores. According to the invention the foundry moulds and cores can be manufactured of a fluid moulding mixture containing a foaming agent apart from said ingredients. To enhance the strength of the moulds and cores the mixture can also contain a water-binding addition, such as cement or carbamide.

United States Patent [191 Lyass et al.

[ 5] Apr. 16, 1974 METHOD OF PRODUCING FOUNDRY MOULDS AND CORES [76]Inventors: Abram Moiseevich Lyass,

Sharikopodshipnikovskaya ulitsa, 2, kv. 146; Pavel Atanasievich Borsuk,Nizhne-Pervomaiskaya ulitsa, 59, kv. 10; Zokhrab Gamid Ogly Usubov, B.Cherkizovskaya ulitsa, kvartal 8-11, korpus 21, kv. 106; ViktorGeorgievich Kuznetsov, 5 Kozhukhovskaya ulitsa, 10, kv. 36; NaumYakovlevich Kagan, 2 ulitsa Mariinoi roschi, 14v, kv. 22, all of Moscow;Jury Alexeevich Razumeev, ulitsa Kolontsova, 7, kv. 6, MytischiMoskovskoi Oblasti; Vladimir Mironovich Bortnik, Eiskaya ulitsa, 9, kv.26; Isai Volfovich Korenbljum, Veernaya ulitsa, 3, korpus 4, kv. 112,both of 9 Moscow, all of U.S.S.R.

[22] Filed: Apr. 11, 1972 [21] Appl. No.: 243,066

[52] U.S. Cl. 106/382, 106/3835, 106/38.5 R, 106/69 [51] Int. Cl B28b7/34 [58] Field of Search 106/3835, 38.3, 38.5 R, 106/389, 38.2, 69

[5 6] References Cited UNITED STATES PATENTS 3,032,425 5/1962 Leach106/389 1/1969 Liass et a1. 106/3835 FOREIGN PATENTS OR APPLICATIONS.

573,171 11/1945 Great Britain 710,099 6/ 1954 Great Britain 714,7289/1954 Great Britain Primary Examiner-Lorenzo B. Hayes Attorney, Agent,or Firm-Holman & Stern [5 7] ABSTRACT A method of producing foundrymoulds and cores comprising the steps of preparing a mixture containinga moulding sand, an ingredient chosen from the group which consists ofligno sulphonate of an alkali, alkaliearth metal, ammonium and theirmixture as a binder, a material containing aluminate of an alkali metalas a hardener and water, making moulds and cores from said mixture andweathering to harden. The material containing aluminate of an alkalimetal is an intermediate product obtainable in the production ofaluminum oxide from bauxite or nepheline ores. According to theinvention the foundry moulds and cores can be manufactured of a fluidmoulding mixture containing a foaming agent apart from said ingredients.To enhance the strength of the moulds and cores the mixture can alsocontain a water-binding addition, such as cement or carbamide.

5 Claims, No Drawings METHOD OF PRODUCING FOUNDRY MOULDS AND CORES Thepresent invention relates to the field of foundry work and moreparticularly to a method of producing foundry moulds and cores by usinga self-hardening moulding sand or mixture.

Well known is a method of producing moulds and cores from a mouldingmixture containing moulding sand, sodium silicate and dicalciumsilicate. Hardening of this mixture is due to interaction between sodiumand dicalcium silicates which results in manufacturing strong cores andmoulds (see, for example, French Pat. No. 1,342,529). This prior-artmethod proves successful in practice though it presents some problems,such as: more difficult decoring of castings, friability of hardenedmoulds and cores and difficulties related to hardening rate control.

To overcome these problems a method was devised comprising theproduction of cores and moulds from a self-hardening moulding sandcontaining ground refractory material, ligno sulphonate of an alkali,alkaliearth metal, ammonium or their mixture, cement and an acid liquorresulting from pyrolysis of wood pulp at gas producing plants. Forproducing a fluidmixture a foaming agent was added to the above sand(see, for p Swedish Ba t, No. 323,476, C]. 31b 16).

However, this method also presents some difficulties,

such as comparatively low hardening rates .of the moulds and coresproduced thereof (the hardening process lasts for 5-12 hours) and lowstrength which does not exceed 0.6 kg/cm within 1 hr after theirproduction.

Commonly known also is a method of making foundry moulds and cores of amoulding sand containing ground refractory material, ligno sulphonate ofan alkali, alkali-earth metal, ammonium or their mixture as a binder, acompound of hexavalent chromium as a hardener, a foaming agent andwater.

The problems associated with the above method are attributed in thefirst place to low gas permeability of the moulds and cores produced bythe above technique necessitating thereby drying at a l50-200 Ctemperature for 1.5-2 hrs.

Moreover, the compound of hexavalent chromium employed as the hardenerbeing toxical, some caution is necessary in the use of this hardener.

It is an object of the present invention to overcome or at least todiminish the above difficulties.

The principal object of this invention is to provide such a method ofproducing foundry moulds and cores of a self-hardening sand, which willensure substantial enhancement of both mechanical-and-physicalproperties of said moulds and cores and of their hardening rate.Besides, it would be preferable to avoid the packing operation in makingfoundry moulds and cores.

According to the invention, this is achieved by the fact that inpreparing a mixture containing moulding sand, ligno sulphonate of analkali, alkali-earth metal, ammonium or their mixture as a binder, amaterial containing alkali metal aluminate is employed as a hardener.

Due to the reaction between ligno sulphonate and aluminate of an alkalimetal, the foundry moulds and cores produced thereof feature highstrength, the hardening process being effected at a perceptibly higherrate.

In a preferred embodiment of the present invention it is useful toemploy the alkali metal aluminate amounting to within 0.5-5.0 percent ofthe weight of the moulding sand. This will ensure the maximum possiblestrength of the foundry moulds and cores produced thereof. Soundpractice would be to choose a sodium-aluminate-containing material forthat purpose, the materials being most commonly used in the industry.Thus, an intermediate product obtained in the production of aluminiumoxide from bauxite or nepheline ores would be preferable for use as thematerial containing an alkali metal aluminate. The above product isproduced by sintering bauxite or nepheline ores mixed with sodiumcarbonate and limestone at a temperature of 1,200 C. Next the resultingproduct hereinafter referred to in the description as accordingly abauxite sinter or a nepheline sinter is cooled and ground to grain sizeof 0.3-1 mm.

The foregoing grain size is preferred with the mould and core makingtechnique conforming to the present invention.

The chemical and mineralogical composition of the sinters are presentedin the Table.

With the use of these sinters both the mixture strength and itshardening rate depends on the amount of sodium aluminate containedtherein. Naturally the higher the content of sodium aluminate in saidsinters, the higher are the strength and hardening rate of the mouldingmixture.

The quantity of the sinter which should be introduced into the mixturein order to secure the requisite strength and hardening rate of themoulds and cores ranges from 3 to 10 parts by weight to provide thesodium aluminate content of 0.5 to 5 percent respectively of themoulding sand weight.

According to this invention, ligno sulphonate of an alkali, alkali-earthmetal, ammonium or their mixture is employed as a binder. The mostwidely known material containing sodium, calcium, ammonium lignosulphonate or their mixture is the waste product resulting from theproduction of cellulose from wood pulp by the sulphite process.Hereinafter in the description the product will be referred to as asulphite alcohol waste liquor.

Maximum efficiency is attained with the ligno sulphonate content rangingfrom 1 to 5 percent of the weight of the moulding sand.

The sulphite alcohol waste liquor employed in the moulding mixture inaccordance with the invention comes from the industry either in a liquidform or in the form of dry concentrates, the ligno sulphonate contentvarying from 45 to 97 percent by weight. The higher the ligno sulphonatecontents in the sulphite alcohol waste liquor, the smaller shall be itsamount in the mixture to attain the same strength characteristics of themoulds andcores. The ligno sulphonate content in the liquid sulphitealcohol waste liquor may be characterized by its specific gravity.According to the present invention, the moulding mixture containscommonly an aqueous solution of the sulphite alcohol waste liquor ofaspecific gravity of 1.10-1.27 g/cm, the ligno sulphonate content of thesolution ranging from 25 to 55 percent by weight which corresponds toits content in the mixture of from 1 to 5 percent of the weight of themoulding sand.

Cited below are exemplary embodiments of this invention in which thesulphite alcohol waste liquor is nate of an alkali, alkali-earth metal,ammonium or their mixture in accordance with the invention, is ofparticular importance for fluidmoulding sands which, apart fror n themoulding sand, said ligno s ulphonate and the Chemical composition, byweight Sinter SiO Ano Fe,O CaO Na,0

Bauxite sinter -12 29-31 10-11 -22 21-25 Nepheline sinter Mineralogicalcomposition, by weight Dicalcium silicate Sodium Aluminate Sodiumferrite Bauxite sinter 40-55 30-45 8-17 Nepheline sinter 70-80 10-25 2-8EXAMPLE 1 100 parts by weight of quartz sand are mixed for 2 1.5-2.0min. with 4.0 parts by weight of a sulphite alcohol waste liquor of aspecific gravity of 1.24-1.26 g/cm containing accordingly 48-52 percentby weight of ligno sulphonate, and tempered with 2.0 parts by weight ofwater. Then 2.5 parts by weight of a bauxite sinter and 40 percent byweight of sodium aluminate are added to the mixture and stirring iscontinued for 0.5-2.0 min.

The mixture being charged in a core or moulding box, a mould or a coreis produced in a conventional manner. Next the mould or the core is leftto harden in air.

The compression strength (kg/cm of the moulding sand amounts to:

after air hardening for 1 hr. after air hardening for 3 hrs. after airhardening for 24 hrs.

The strength of the moulds and cores produced thereof can be improved byintroducing a known addition into the hardener to bind water in themixture.

As to the suitable additions, use may be made of loam, bentonite, cementor gypsum to be introduced in amounts ranging from 0.5 to 5 percent ofthe weight of the moulding mixture.

EXAMPLE 2 100 parts by weight of quartz sand are mixed for 1-2 min. with4.0 parts by weight of a sulphite alcohol waste liquor of a specificgravity of 1.24-1.26 g/cm containing accordingly 48-52 percent by weightof ligno sulphonate, and with 2.0 parts by weight of water. Then 2.5parts by weight ofa bauxite sinter, containing A method of hardening thebinder ligno sulphomaterial containing alkali metal aluminate, include afoaming agent introduced in the mixture in quantities large enough topass the mixture to a fluid state.

The amount of the foaming agent ranges within 0.4-1 percent of theweight of the moulding sand.

The foaming agents added to the moulding mixture may constitute anion,cation and nonionogenic surfaceactive materials. These may be alkyl arylsulphonates, alkyl sulphonates, primary and secondary alkyl sulphates,the products of oxyethylation of alcohols, phenols, amines, quaternaryammonium compounds of long-chain fatty amines.

The most suitable foaming agent is an anion-type surface-activecompound, such as sodium alkyl aryl sulphonate ensuring the productionof a fluid moulding mixture featuring high flowability and the requisitefoam stability in the mixture, i.e., the property to retain mobilityduring the length of time needed to pour the mixture into core andmoulding boxes. An advantage of the fluid moulding sand is its highflowability by which virtue the conventional sand compacting techniquecan be dropped to be replaced by pouring the sand into the core boxesand on patterns during the production of the moulds and cores.

It should be noted that ligno sulphonate of an alkali, alkali-earthmetal, ammonium or their mixture employed according to the invention inthe manufacture of moulds and cores as a binder, possesses some foamingcapacity, being thereby capable of imparting the mixture a betterflowability when it is subjected to intense stirring during preparation.

By using said binder and by adding a small amount of the foaming agentthe fluid moulding mixture is especially simple in production.

EXAMPLE 3 A fluid mixture can be prepared by mixing parts by weight ofquartz sand, 4.0 parts by weight of a sulphite alcohol waste liquor of aspecific gravity of within 1 hr. after manufacture within 3 hrs. aftermanufacture within 24 hrs. after manufacture Conforming to thisinvention, the overall strength of the cores can be increased bycarbamide introduced into the moulding mixture.

The best results are obtained when adding from 0.8 to 2.0% of carbamide(of the weight of the moulding sand).

We have found that the use of carbamide for improving the strength ofthe moulds and cores made from a fluid self-hardening sand containingthe foaming agent, can reduce appreciably sand humidity; the amount ofwater added to the sand can be also decreased by 1.0-2.0 percent of theweight of the moulding sand.

EXAMPLE 4 100 parts by weight of quartz sand are mixed with 4.0 parts byweight of a sulphite alcohol waste liquor of a specific gravity of1.24-1.26 g/cm containing accordingly 48-52 percent by weight of lignosulphonate, the liquor being preliminarily tempered with 1.0 parts byweight of water in which 0.8 parts by weight of powdered carbamide weredissolved.

Within 1.5-2 min. 2.5 parts by weight of a bauxite sinter containing 40percent by weight of sodium aluminate are introduced into the mouldingmixture.

The moulds and cores made from said mixture featured the followingcompression strength (kg/cm ufter air hardening for l hr. after airhardening for 3 hrs. after air hardening for 24 hrs.

wuu

incur position disclosed in Example 4 are 0.6 parts by weight of afoaming agent sodium alkyl aryl sulphonate. After the moulding mixturehas passed to the fluid state 2.5 parts of a hardening agent a bauxitesinter, containing 40% by weight of sodium aluminate are introduced intothe sand.

Said moulding mixture ensures the following compression strength (kglcmof the moulds and cores produced thereof:

after air hardening for 1 hr. 3; after air hardening for 3 hrs. 6.5;after air hardening for 24 hrs. [2.0.

An important merit of the present invention consists in that thestrength of foundry moulds and cores will feature a l.5-2-fold increasealong with a two-fold increase in the hardening rates.

Peculiar to the cores produced in accordance with the invention is goodknockout.

What we claim is:

l. A method of producing foundry moulds and cores comprising the stepsof preparing a mixture containing parts by weight of moulding sand, from1 to 5 parts by weight of an ingredient selected from the group whichconsists of ligno sulphonates: of an alkali, alkaliearth metal, ammoniumand their mixture as a binder, and from 3 to 10 parts by weight of amaterial containing alkali metal aluminate making moulds and cores fromsaid mixture and holding it for air hardening.

2. A method as of claim 1, in which the aluminate of an alkali metal issodium aluminate.

3. A method as of claim 1, in which the material containing aluminate ofan alkali metal is a bauxite sinter.

4. A method as of claim 1, in which the material con taining aluminateof an alkali metal is a nepheline sinter.

5. A method as of claim 1, in which ligno sulphonate is a sulphitealcohol waste liquor.

2. A method as of claim 1, in which the aluminate of an alkali metal issodium aluminate.
 3. A method as of claim 1, in which the materialcontaining aluminate of an alkali metal is a bauxite sinter.
 4. A methodas of claim 1, in which the material containing aluminate of an alkalimetal is a nepheline sinter.
 5. A method as of claim 1, in which lignosulphonate is a sulphite alcohol waste liquor.